During the last year and in the forthcoming years not only will previously undertaken studies be continued on the chromosome findings in bladder cancer, but other areas into which the study has been extended include the determination of centromeric heterochromatin polymorphism in the tumor and somatic (lymphocytes) cells of patients with bladder cancer, the study of the ultrastructure of such heterochromatin in an attempt to possibly establish some specificity in the case of bladder cancers, and undertaking of a comprehensive cytogenetic evaluation of non-invasive and sub-mucosally invasive tumors supplied to our laboratory from about half-a-dozen centers involved in the study of patients with bladder cancer, with major emphasis being placed on follow-up of such patients, both clinically and cytogenetically. This study continues to be concerned with establishing detailed karyotypic aspects of cancer of the bladder with particular emphasis on papillary tumors. Cytogenetic criteria of help to the clinician in predicting possible recurrence of papillary tumors, such as the presence of marker chromosomes and other structural anomalies, have received and will continue to receive primary attention. A study based on the staining of rDNA of the acrocentric chromosomes and the application of this technique to the establishment of subtle translocations involving such chromosomes is now being utilized in our laboratory. Another aspect of the study is correlation of transitional cell cancers of the bladder and a correlation of the cytogenetic findings with therapeutic and biologic behavior of these cancers. Emphasis is being put on the changes involving certain chromosome groups, e.g., #1 and #14, as biologic indicators of the behavior of such tumors.